What pregnant women need to know about COVID and booster shots

Inoculations for immunosuppressed individuals are recommended in the second trimester

Questions regarding COVID-19 booster shots for pregnant women have been pouring in across San Francisco’s health care network, city officials said this week.

But there’s not much confusion. Health experts resoundingly agree: Women who are pregnant, or thinking about becoming pregnant, should get vaccinated and receive a booster shot.

Monica Gandhi, who heads up the Division of HIV, Infectious Diseases, and Global Medicine at UC San Francisco, says the second trimester is the ideal time for pregnant women to get a booster.

“I recommend getting a booster well after the first trimester, into the second trimester. You want to protect the fetus when the placenta is fully formed so antibodies can cross over” to the fetus, Gandhi said. “That’s also a good time because that’s when pregnant women are more immunosuppressed.”

Pregnant people fall under the high-risk category currently prioritized for booster shots in San Francisco, Dr. Naveena Bobba, deputy director of health in San Francisco, said at a hearing Tuesday. This group is traditionally regarded as high-risk because a pregnant body will immunosuppress foreign antigens to protect a fetus.

“This is a known phenomenon. We always consider pregnant women as immunosuppressed individuals,” Gandhi said.

The Centers for Disease Control and Prevention recommends the COVID-19 vaccination for everyone 12 and older, including those who are pregnant, breastfeeding, trying to get pregnant or might become pregnant in the future. But there isn’t official guidance on when a booster should be administered.

Previously, the CDC recommended boosters for people who got the Pfizer vaccine and faced a higher risk of infection. On Thursday, CDC expanded its recommendation to include Moderna recipients who are high-risk and all Johnson & Johnson recipients as well.

CDC advisers on Thursday also approved “mix-and-match” booster shots to increase antibodies to fight the coronavirus. For individuals who got the Johnson & Johnson vaccine, health experts including Gandhi have recommended individuals get the Moderna or Pfizer shots, which both contain mRNA and have shown to produce more antibodies. Many studies have shown few adverse effects associated with getting a different booster shot from an individual’s initial vaccination series.

While experts agree a booster shot is a good idea for pregnant people, especially those in high-transmission communities, there’s some variance on exactly when a booster should be administered.

“The sooner you get the booster the better. Earlier booster means a lower likelihood of breakthrough, which will reduce risk during preterm and early birth,” said Dr. Peter Chin-Hong, professor in the UCSF Health Division of Infectious Diseases.

A recent large study by UCSF researchers showed that the risk of having a very preterm birth, which occurs at less than 32 weeks of gestation, was 60% higher for people infected with COVID-19 at some point in their pregnancy.

For pregnant individuals with other underlying health conditions including hypertension or diabetes, the risk of preterm birth is up to 160% higher, the study found.

“As a pediatrician, I’m always a little worried about extra stuff in pregnancy that doesn’t need to be going on, but this is one of those things that definitely need to be going on,” said Dr. George Rutherford, infectious disease expert at UCSF. “If you’re planning to get pregnant, go get your booster now.”

But there’s another problem: Many pregnant women have not received their first shot. Just over 34% of pregnant individuals in the United States were vaccinated before or during their pregnancy as of Oct. 16, according to the CDC.

Part of that hesitation is expected to be tied to a swarm of misinformation over the past year around COVID-19 vaccines and fertility. But zero safety concerns have been associated with the vaccine and fertility of pregnancy, according to the CDC. “There is no link with infertility whatsoever,” said Gandhi.

“The elephant in the room is not about boosters as much as just getting pregnant individuals vaccinated in the first place,” said Chin-Hong. “The first vaccine is the most important one.”

Still, boosters for pregnant women are a no-brainer, said Chin-Hong. In fact, vaccinated mothers can pass on antibodies that fight the COVID-19 virus to fetuses through the bloodstream and even after birth through breastfeeding.

“Everyone looking at this virus believes pregnancies are eligible as a medical condition for a booster shot,” Chin-Hong said. “The vaccine is not a live virus at all, so we aren’t worried about giving this at any time during pregnancy.”

Studies are underway examining vaccine efficacy and impacts on children between ages 2 to 5 and infants between 6 months and 2 years old. Currently, the Pfizer vaccine is only approved for children as young as 12, and regulators are expected to approve the vaccine for children between ages 5 and 11 in coming weeks.


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